Hydrogen storage materials or media (HSMs) are a class of chemical compounds containing hydrogen in a chemically or physically bound form. There is a particular current interest in HSMs for hydrogen storage applications and in particular, for hydrogen-powered vehicles for use in a ‘hydrogen economy’. This use requires an on-board source of hydrogen fuel. Hydrogen storage for transportation must operate within minimum volume and weight specifications, supply enough hydrogen for sufficient distance, charge/recharge near room temperature, and provide hydrogen at rates fast enough for fuel cell locomotion of automotive vehicles. Therefore, in order to create a useful on-board source of hydrogen fuel, an efficient method of storing the hydrogen is required.
Despite optimism over the last three decades, a hydrogen economy remains a utopian vision. The US Department of Energy (DOE) Basic Science group recently summarized the fundamental scientific challenges that must be met before a hydrogen economy becomes viable. In Basic Research Needs For The Hydrogen Ecomony, US DOE Report, May 2003, the following design criteria were identified for a viable HSM:                (i) High hydrogen storage capacity (min 6.5 wt % H).        (ii) Low H2 generation temperature (Tdec ideally around 60-120° C.).        (iii) Favorable kinetics for H2 adsorption/desorption.        (iv) Low cost.        (v) Low toxicity and low hazards.        
Virtually all HSMs used in prior art technologies have been known for several decades, and none of them meet all five of the criteria listed above. For example, a number of alloys such as FeTi, Mg2Ni and LaNi5 satisfy criteria (2)-(5) but fail on criterion 1, containing only a few wt % hydrogen when fully loaded. Li3BeH7 reversibly stores 8.7% hydrogen by weight, but is highly toxic, thereby failing on criterion (5). Materials such as LiBH4 and NaBH4 react rapidly with water (hydrolysis) to release large amounts of hydrogen, but this process is chemically irreversible. Many other materials satisfy criteria (1), (2), (4) and (5), but not criterion (3).